1. Field of the Invention
The present invention relates to a grinder for grinding an outer surface of a roll, such as a paper machine roll, in particular a tissue cylinder or a machine glazed cylinder.
2. Description of the Related Art
Cylinders having a smooth surface must be reground from time to time. Hitherto roll grinding machines or so-called profile grinding machines have been used to grind great tissue (yankee) or machine glazed cylinders. Such profile or tangential grinding machines grind a smooth contour while traversing the rotating cylinder. However, profile machines of this kind weigh in excess of 4 tons, causing transport and space problems. Profile or tangential grinding is much more involved than a polishing procedure which is used to remove smaller surface damage and roughness. Furthermore, the use of profile grinding machines require considerable reinstallation work. Profile or tangential grinding machines, which are used to recondition great tissue (yankee) or machine glazed cylinders, are of the form of large bench type grinders that have to be installed, leading to the following disadvantages:
heavy and bulky to ship around the world
long transport routes due to sea freight
take a relative long time to install and prepare the equipment underneath the cylinder
major paper machine components must be removed and reinstalled to allow space for the grinder.
Polish grinding machines, are used for polishing, having lower transport costs and require less installation and dismounting time than grinding machines. Such polish grinding machines are small and have a weight of about 0.5 tons. Polish grinding machines are usually embodied by belt or band grinding machines as disclosed in WO 9803304 and WO 9302835. Machines of this kind provide a sufficiently great power but are not used to change the contour of the cylinder. They are limited to compensating for scratches, markings and the like. Band grinding machines are mounted on the scraping blade holder of the cylinder and can, without greater expenditure, be laid out for traversing along the cylinder.
A disadvantage of polish grinding machines is that they do not influence the contour or the concentricity of the cylinder and are pneumatically pressed against the cylinder with constant pressure. In contrast to profile grinding machines, where a reference is given by the machine bed or by a physical reference plane on the grinding machine, polish grinding machines are not provided with such a reference. In particular, the scraper blade cannot be used as a reference when, the contour or the concentricity of the cylinder is to be reestablished.
The present invention provides a grinder having the basic structure of the polish grinding machine as disclosed in WO 9803304 and WO 9302835, but by which profile grinding can also be carried out.
A measuring system associated and displaceable with the grinding mechanism is provided for determining the position of the displaceable grinding mechanism relative to the roll and relative to at least one reference line provided outside of the roll. The system and mechanism is adjusted parallel to the axis of the roll, with the relative position being determined in a plane, preferably perpendicular to the reference line. The grinding effected by the grinding mechanism is controlled on the basis of the measurement values obtained from the measuring system.
With a virtual reference a corresponding control of the application force or contact pressure force of the polish grinding or profile grinding machine is possible. Even if the grinder is used for profile grinding, due to the virtual reference that is provided, the basic structure can principally be the same as with a usual polish grinding machine, such as a polish grinding machine disclosed in WO 9803304 and WO 9302835, the disclosures of which are hereby incorporated herein by reference. The measuring system is preferably a laser measuring system.
In accordance with a further embodiment of the present invention at least one reference line is provided as a wire spanned parallel to the axis of the roll. In practice, the grinding mechanism is preferably controlled so that only elevations are removed.
When at least two parallel reference lines are provided, the measuring system can additionally be laid out for determining the inclination of the grinding mechanism in a plane perpendicular to the reference lines and/or for determining the angular position of the roll. The measuring system may include a triangular path measuring device, for carrying out measurements by triangulation.
In accordance with another embodiment of the present invention, the measuring system determines the outer surface contour of the roll. The grinder can be controlled so that measurement and grinding cycles are executed in parallel or alternately. However, it is preferred to control the grinder so that measurement and grinding cycles are executed alternately. The grinding mechanism itself is preferably a band grinding mechanism.
According to yet another embodiment of the present invention the grinder is controlled for profile grinding. The grinding mechanism is mounted on a scraper blade holder associated with the roll or on a rail temporarily replacing the scraper blade, and displaceable along the scraper blade and rail, respectively.